Pump action hand foamers are well-known in the art. Generally they comprise a container for holding foamable liquid and a foam-generating device, typically comprising a plunger-operated pump, mounted in the neck of the container and having an inlet such as a dip tube communicating with the container interior to draw liquid into a pump chamber. To generate foam, the liquid must be mixed in appropriate proportion in air under turbulent conditions, with regulation as necessary to make the bubble size in the foam reasonably uniform. This is technically demanding and commercially important, because wet or non-uniform foams have low consumer acceptability.
One well-established pump type has separate pump cylinders for the air and liquid, with respective inlet valves and pistons carried by a single plunger. The corresponding air liquid outlets open into a mixing chamber downstream of the pump chamber—usually in the neck region of the dispenser above the pump cylinders—and the thus-mixed, liquid and air passed through one or more meshes to regulate the foam. These dispensers mix well-defined proportions of air and liquid, but they are large and expensive, and not generally susceptible of a lock-down structure so that a separate cap must be provided. See e.g. EP-A-0565713, EP-A-0613728, WO97/13585 and EP-A-1190775.
Separately, it has been proposed to make a pump foamer by drawing both air and liquid together into a pump chamber operated by a piston, under conditions promoting turbulent mixing so that the chamber fills with foam, the foam then being expelled through the pump outlet e.g. through a plunger stem. In US2007/0040048A a conventional piston/cylinder plunger pump is fitted with a dip tube extending down to the container bottom, where the dip tube has a small hole, and up again to the top of the container where the dip tube end opens in the air above the liquid in the container. The pump action draws air rapidly through the dip tube, entraining a small proportion of liquid through the entry hole at the bottom of the container as it passes towards the pump. WO01/39893 describes introducing air through a separate air intake conduit defined by an outer cylindrical jacket fitting around the pump cylinder with some clearance and opening inside the container neck, so that air from the container interior can pass down between the jacket and pump body to the inlet region, entering beneath an inlet flap valve side-by-side with liquid from a conventional dip tube. WO2008/133491 describes an inlet fitting which adds an extra ball valve beneath a pump inlet valve, and vents in air from the container interior between the valves to mix with the liquid. WO2011/144861 also describes double inlet ball valves, with air inlet jets and a mixing mesh between them.